1. Field of the Invention
This invention relates to a method for repeatedly dispensing a predetermined amount of a test liquid onto a chemical assay element such as a chemical assay slide by using a dispenser.
2. Description of the Prior Art
When the amount of a specific chemical ingredient in a specimen of a liquid such as the body fluid of an organism, e.g. blood or urine, is to be determined by using a chemical assay element, such as a chemical assay slide, it is necessary to measure out a predetermined amount of the liquid specimen precisely and supply it to the chemical assay element. For this purpose, dispensers such as those supplied by Eppendorf (e.g. No.4780) and Nichiryo (e.g. model 8100) have been used widely.
When blood, blood plasma or the like is in contact with air for about 30 seconds, it begins to coagulate. When a dispenser is used to supply repeatedly a coagulative liquid specimen like this, the liquid coagulates at the tip of the nozzle of the dispenser a short time after the test liquid is drawn in and left there. In such cases, it is difficult to dispense the liquid specimen. For example, under the temperature of 24.degree. C. and the relative humidity of 40%, blood coagulates after it is left in the dispenser for about 40 seconds and a certain kind of commercially-available controlled serum coagulates after it is left there for about 3 minutes. Accordingly, in order to supply such a coagulative liquid to a chemical assay element, it is necessary to conduct the dispensing operation within a short time before coagulation begins.
However, the dispensing operation for a single test liquid may take more than several minutes. The dispenser is often used in combination with an automatic analyzer. In such cases, it is not always possible to dispense the test liquid continuously.
An Automatic analyzer often has an incubator in order to allow a chemical reaction necessary for assay to take place. A plurality of assay elements like assay slides, assay tapes or assay cells can be passed through the incubator continuously if the time required for each assay element to pass therethrough is constant. Therefore, in general, the dispensing operation of the liquid specimen can be conducted continuously in these situations. However, if the time required for each assay element to pass through the incubator differs according to the assay items (ingredients to be tested for), the dispensing of the liquid specimen may not always be conducted continuously.
The automatic analyzer disclosed in Japanese Unexamined Patent Publication No. 61(1986)-294368 (Sugaya) has a plurality of incubation chambers each of which is adapted to contain a chemical assay slide. Therefore, in this analyzer, each slide can be maintained at a constant temperature for a desired period. In order to conduct analysis operations efficiently, i.e. to conduct as many analysis operations as possible within a predetermined time, by using such an automatic analyzer, it is desirable that the incubation chambers be kept filled with the slides. If there is a vacant incubation chamber sometime after a certain portion of the liquid has been dispensed and the chamber has been filled with the slides, the next portion of the liquid is dispensed to an assay slide which will be inserted into the vacant incubation chamber. After still another chamber is vacated, the remaining portion of the liquid specimen will be dispensed to a chemical slide.
In such cases, the test liquid is held within the dispenser from the first dispensing (discharging) operation to the next dispensing (discharging) operation. If the liquid coagulates during this period, it will be difficult to dispense the liquid . That is, if the liquid coagulates, no liquid may be discharged from the nozzle or an excessive amount of the liquid may happen to be discharged abruptly therefrom, because the piston, the pump or the like continues to operate in spite of the interruption of the discharge.
Even when there are vacant incubator chambers, the liquid has to be held within the dispenser for a period of time until a dispensing (discharging) operation takes place, if the assay slides or the like are not prepared in good time due to certain accidents. If the liquid specimen coagulates in these cases, dispensing of the liquid will be difficult.